The statements in this section merely provide background information related to the present disclosure and not constitute prior art.
Technical standards established for compressing video data presently include H.261, H.263, H.264, MPEG-2, and MPEG-4. According to the existing video compression technologies, encoding each image is carried out after dividing the same into fixedly sized macroblocks which are composed of rectangular 16×16 pixel areas of a luminance or luma component and rectangular 8×8 pixel areas of a chrominance or chroma component. All of the luma and chroma components of the respective macroblocks are spatially or temporally predicted, and the resultant predicted residuals undergo transform, quantization, entropy coding and the like before they are eventually compressed.
An encoding apparatus by the H.264/AVC compression standard subdivides each macroblock into blocks of smaller sizes 16×16, 8×8, and 4×4 to enter an intra prediction encoding wherein 16×16 pixel blocks are processed in one of four prediction modes and 8×8 pixel blocks and 4×4 pixel blocks in one of nine prediction modes. As for an inter prediction encoding, each macroblock may be first divided into blocks of pixel sizes 16×16, 16×8, 8×16, 8×8, 8×4, 4×8, and 4×4 before the inter prediction encoding. Transform is carried out in units of 8×8 or 4×4 pixel blocks, and quantization of transform coefficients utilizes a scalar quantization.
H.264/AVC transmits quantization parameters (QP) in units of a slice or macroblock. Transmitting QP in unit of a slice unit is carried out with differential quantization parameters calculated by using Equation 1.ΔQPslice=QPcur−26−ΔQPPPS   Equation 1
In Equation 1, QPcur is a quantization parameter used in a current slice, and ΔQPPPS is a differential quantization parameter transmitted to a picture parameter set (PPS). ΔQPPPS is equal to the subtraction of 26 from a quantization parameter value inputted by a user in encoding, as expressed in Equation 2.ΔQPPPS=QPuser−26   Equation 2
The quantization parameter transmitted in units of a macroblock encodes a differential value between a quantization parameter value of a previously encoded macroblock and a quantization parameter value of a current macroblock, as expressed in Equation 3.ΔQPMB=QPcurMB−QPprevMB   Equation 3
The quantization parameter transmitted in units of a macroblock is encoded adaptively according to a block type and a coded block pattern (CBP). In the case of intra blocks, with respect to all macroblocks, a differential value of a quantization parameter calculated by Equation 3 is encoded. In the case of inter blocks, a CPB value is checked to determine whether a quantization parameter is encoded. If or when a current macroblock has no quantized transform coefficient data to be decoded, a quantization parameter is not transmitted. If or when there is a CBP, a quantization parameter is transmitted by using Equation 3.
However, an H.264/AVC-based quantization parameter transmission method is designed only with macroblock considered to be the basic encoding unit. The inventor(s) has noted that in line with increasing resolution of videos used for encoding, a basic encoding unit is not limited to a macroblock, and the use of an extended macroblock is considered. The inventor(s) has experience that there is a need for an optimal quantization parameter encoding method suitable for this.